As a class of chemicals, dithiocarbamates and methods for their synthesis have been known for over a hundred years. The alkaline earth-salts of dithiocarbamates, such as sodium and potassium, and the heavy-metal salts of dithiocarbamates, such as zinc and magnesium, have found wide-spread use in agriculture and industry as important microbiocidal and fungicidal compositions. [See, e.g., U.S. Pat. No. 1,972,961] The sodium and potassium salts of dithiocarbamic acids have primarily been used in liquid form, while the heavy metal zinc and magnesium salts are presently used as dry powders dispersed in water or in water-in-oil emulsions.
One particularly valuable microbiocidal product that has been on the market for many years is a liquid combination of equal parts by weight of sodium dimethyldithiocarbamate (referred to hereafter as "SDDC") and disodium ethylene bis-dithiocarbamate referred to hereafter as ("NABAM") (30%, by weight, total active ingredients). This liquid material is used in many industries for controlling the growth of bacteria, yeast and fungi, such as those found in industrial recirculating water cooling towers, air washers, evaporative condensers, pulp and paper mills, drilling fluids, secondary and tertiary petroleum recovery, cane and beet sugar mills, and the like. This compound has also been used for controlling the growth of algae in some of these applications.
The chemical instability of compounds containing ethylene bis-dithiocarbamate (referred to hereafter as "EBDC") was recognized at about the time of the discovery of their use as fungicides. [See, e.g. A. E. Dimond et al., Phytopathology (1943); U.S. Pat. No. 2,317,765]. This instability manifests itself during manufacture and storage of liquid or dry products containing disodium ethylene bis dithiocarbamate ("NABAM"). For example, J. W. Heuberger, et al, Phytopathology (1943) reported the use of a zinc sulfate--lime mixture to stabilize the chemical instability associated with EBDC salts. Various other means have been proposed to stabilize NABAM. For example, U.S. Pat. No. 3,449,386 discusses using 1,8,3,6-diendomethylene-1,3,6,8-tetrazacyclodecane to stabilize the heavy metal salt, manganous ethylene bis dithiocarbamate. Cuprous compounds have also been employed to stabilize heavy metal salts of zinc, manganese, or iron ethylene bis-dithiocarbamate, according to U.S. Pat. No. 3,523,960. Similarly aqueous formaldehyde (U.S. Pat. No. 3,856,836) and cinnamic aldehyde (U.S. Pat. No. 4,185,113) have been added to precipitated manganese and zinc salts of EBDC to provide enhanced chemical stability. U.S. Pat. No. 4,217,293 discloses the blending of paraformaldehyde with dry manganese ethylene bis dithiocarbamate [MANEB] for stabilizing purposes.
These methods of imparting stability to compounds containing EBDC involve the use of a variety of additives to stabilize the heavy metal salts of EBDC. The disadvantage of these approaches to stabilizing metal salts of ethylene bis-dithiocarbamate are that these additives, though they may impart stabilizing properties, are also diluents or adulterants of the microbiocidal or fungicidal activity of the compounds containing EBDC.
Few efforts have focused on imparting stability to the presently most useful EBDC for microbiocidal use, i.e., the disodium EBDC, or NABAM. U.S. Pat. Nos. 3,050,439 and 3,050,532 disclose methods for producing anhydrous NABAM by spray drying method. The disadvantages of the spray drying process of '439 are that the process must be under very careful control or decomposition will result; and that, once produced, the anhydrous salt must be kept away from moisture or it will revert to the hydrate, decomposing in the process.
There remains a continuing need for improved microbiocidal compounds for a variety of industrial uses which are capable of efficiently controlling growth of microorganisms and yet can be readily manufactured and used in industry.